The invention relates to a process and apparatus for controlling an engine-braking system of an internal combustion engine driving a vehicle that is provided with brake flaps arranged in the exhaust-gas lines and constant-throttle valves provided in the cylinder heads. In the event of an activation of the engine-braking system, the brake flaps are transferred to their closing position and the constant-throttle valves to their opening position.
In a device of the relevant generic type known from German Patent Specification No. 3,428,626, the brake pedal of the vehicle is connected to a control cylinder which is designed in such a way that, with an increasing actuation of the brake pedal, successively first the constant-throttle valves are opened and only thereafter is the brake flap arranged in the exhaust-gas line closed. So that the maximum engine-braking capacity can be achieved, the brake pedal therefore has to be actuated sufficiently far.
An object on which the invention is based is to provide a device of the type referred to above in which actuation of the engine-braking system is simplified and the possibility of activating the engine-braking system below a predetermined limit value for the speed of the internal-combustion engine is excluded.
This object is achieved by providing an arrangement wherein an accumulator connected to a fluidic line system having first and second branches, the at least one brake flap being actuable by fluid pressure in the first line branch and the constant pressure valves being actuable by fluid pressure in the second line branch, wherein, above a predetermined engine speed threshold valve, the first valve arrangement is in its first switch position when a switch unit is actuated for activating the engine-braking system and when the pressure in the line portion between the second valve arrangement and the constant-throttle valves is simultaneously above a predetermined first limit pressure,
wherein the second valve arrangement is in its first switch position either when, above the predetermined engine speed threshold value, the switch unit is actuated for activating the engine-braking system or when, after the release of the switch unit, the pressure in the line portion between the first valve arrangement and the actuator for actuating the brake flap is above a second limit pressure, the second limit pressure being lower than the first limit pressure,
and wherein the two valve arrangements are in their second switch position when the speed of the internal-combustion engine is below the predetermined threshold value.
The device according to the invention provides an engine-braking system which can be activated or deactivated completely in a simple way by the vehicle driver. At the same time, there is always the guarantee that, during activation, first the constant-throttle valves are opened and only thereafter are the brake flaps in the exhaust-gas line closed, or, in the opposite instance, during deactivation first the brake flaps are opened and only thereafter are the constant-throttle valves closed again. An operating state in which the internal-combustion engine works normally, but the brake flap is still closed, consequently cannot arise. There is therefore no possibility of damage to the internal-combustion engine as a result of too high a pressure level in the exhaust-gas line because of simultaneously closed brake flap and constant-throttle valves. This applies especially to the use of reduced-gap brake flaps, that is to say brake flaps which, when in their closing position, still leave free only an extremely small exhaust-gas line cross-section. At the same time, with the device according to the invention, the possibility that the internal-combustion engine will stop as a result of a sudden decrease in speed is excluded.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.